Fluke Biomedical 943-27 Detector - Manual (Page 21)

Maintenance, Calibration and Troubleshooting
Calibration
4
4-7
Detector Leakage:
1. With the detector connected to the readout device, apply power and allow a 15-minute warm-
up.
2. Record the readout with no radiation sources present. The maximum background current is
approximately 4.0 x 10
-11
amps.
3. Expose the window of the detector directly to light. Read detector leakage. There should be
little difference between this and the previous reading. If there is a significant increase in
readings, the detector window has a light leak and must be repaired before proceeding.
Calibration Source Measurements, General:
1. Remove the detector from the sampling geometry and note the background radiation reading.
In a normal background environment, the background should be less than 4.0 x 10
-11
amperes.
If the background is greater than this, the detector should be replaced. Record the ambient
background radiation value.
WARNING
The following procedure exposes the operator to beta
radiation. Safety glasses must be worn and the amount
of “line of sight” exposure time must be minimized.
2. Remove the source holder end cap. This is the smaller of the two end caps.
3. Insert the detector into the P/N 844-211-1-13,
137
Cs reference source.
4. With the source in place, allow approximately two minutes for the reading to stabilize. Record
the reading displayed on the readout device. The reading should yield a net value, within +/-
2%, of the decay corrected, background subtracted target value provided on the original
calibration data sheet. If the reading is not within +/- 2%, the high voltage may be increased or
decreased as necessary. Once +/-2% agreement is reached, NO FURTHER ADJUSTMENTS
of the high voltage are permitted.
5. Remove the detector from the source holder and re-install the end cap.
6. Re-run the background measurement. The background should remain less than 4.0 x 10
-11
amperes
7. Repeat steps 2 through 5 using the remaining two sources. The reading should yield a net
value, within +/- 6%, of the decay corrected, background subtracted target value provided on
the original calibration data sheet.
Calibration Source Measurements, using Model 960 Digital Radiation Monitoring System:
1. Select the Display Option on the 960 front panel keypad that converts the display units to
raw output from the detector (in amperes).
2. Remove the detector from the sampler.
3. Decay to the present day the “net current” value printed on the calibration data sheet,
under the heading of customer sources, for the Cesium-137 source.
WARNING
The following procedure exposes the operator to beta
radiation. Safety glasses must be worn and the amount
of “line of sight” exposure time must be minimized.
4. Remove the cap marked “Removing this cap will expose user to beta radiation”.
5. Place the Cesium-137 source assembly on the ground with the open side up.
6. Insert the detector into the source assembly.